Woven fabrics that are made from thermoplastic yarns tend to disassemble along the cut edge, when cut into pieces or shapes and subsequently handled during various assembly operations. This disassembly occurs as the result of the untangling of the warp and weft yarns, and is commonly known as raveling.
Raveling significantly reduces the efficiency of subsequent article fabrication operations such as sewing, and seriously reduces the strength of the fabric at its edges. Articles fabricated from fabrics with edges having untangled warp and weft yarns tend to pull apart when sewn together and stressed. This phenomenon is generally referred to as combout. When this deficiency, particularly in strength, occurs in airbags which become inflated by high speed expansion with a hot gas, unacceptable leakage of gas occurs at the sewn seams and could potentially result in burn injuries to persons in close proximity to the inflated airbag.
Various physical procedures have been proposed and adopted to prevent edge raveling. These include fusing the warp and weft yarns along the cut edge by various means during the cutting process. Processes known to be commonly used in this regard are based on hot-die and laser cutting methods. Generally, these methods are limited to cutting one to ten layers of fabric at a time, thus adding significant costs to the production of the finished articles such as automotive airbags.
Airbags typically used in restraint systems in automobiles and other vehicles must satisfy a number of unique and demanding requirements. For example, airbags must have the ability to inflate fully in milliseconds, absorb the impact of the passenger, yet deflate rapidly to provide pneumatic dampening, thus preventing the passenger from being repelled in a rearward direction. Fabrics that are useful for airbag construction are required to be strong, lightweight, packable or foldable into a confined area, and resistant to abrasion.
Typically, conventional airbags meeting the above objectives are made of coated fabrics like neoprene-coated nylons. However, some airbag designs, particularly those intended for passenger side application, may use uncoated fabrics except for those areas which may require reinforcement, such as perimeter seams. The technology described herein is ideally suited to these applications. These otherwise uncoated airbags may optionally contain vent holes to deflate, or preferably rely on the inflating gases escaping through porous, low permeability, non-coated panels such as those described by Block in U.S. Pat. No. 4,921,785. Some of the advantages of the latter option include lower cost, lighter weight, and enhanced packability. The designs using essentially non-coated and low permeability panels require fabric edge reinforcement to allow efficient airbag construction and acceptable inflation performance.